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Article

Relative Rate Constants of Contaminant Candidate List Pesticides with Hydroxyl Radicals

Hilla Shemer,^† Charles M. Sharpless,^‡ Michael S. Elovitz,^§ and Karl G. Linden*^†

Department of Civil and Environmental Engineering, Duke University, Box 90287, Durham, North Carolina 27708, Department of Chemistry, University of Mary Washington, Fredericksburg, Virginia 22401, and Treatment Technology and Evaluation Branch, Water Supply & Water Resources Division U.S. EPA, Cincinnati, Ohio 45268

Environ. Sci. Technol., 2006, 40 (14), pp 4460–4466

DOI: 10.1021/es0602602

Publication Date (Web): June 9, 2006

†

Department of Civil and Environmental Engineering, Duke University.

‡

Department of Chemistry, University of Mary Washington.

Treatment Technology and Evaluation Branch, Water Supply & Water Resources Division, U.S. EPA.

Corresponding author phone: +1 (919) 6605196; fax: +1 (919) 6605219; e-mail: kglinden@duke.edu.

Abstract

The objective of this study was to establish the relative rate constants for the reactions of selected pesticides (linuron, diuron, prometon, terbacil, diazinon, dyfonate, terbufos, and disulfoton) listed on the U.S. EPA Contaminant Candidate List with UV and hydroxyl radicals (·OH). Batch experiments were conducted in phosphate buffered solution at pH 7. All pesticides were found to be very reactive toward ·OH as indicated by rate constant values above 10⁹ M^-¹ s^-¹. Using molinate as a reference compound, k_OH ranged from 2.7 × 10⁹ to 12.0 × 10⁹ M^-¹ s^-¹ for the contaminants while slightly higher values from 2.9 × 10⁹ to 14.3 × 10⁹ M^-¹ s^-¹ were obtained using nitrobenzene as a reference compound. A method was established that accounts for direct photolysis when calculating k_OH using UV/H₂O₂ process for compounds which degrade significantly by a direct photolysis mechanism.